1. Field of the Invention
This invention relates to the manufacture of ingots of fused quartz or fused silica of the type which serve, for example, as preforms for the manufacture of high quality fused quartz or fused silica tubing.
2. Prior Art
My prior patent U.S. Pat. No. 4,188,201 discloses an apparatus for forming a hollow ingot within a cylindrical housing rotatable around a horizontal axis. In that apparatus, the cylindrical interior surface of the housing is lined with a layer of granular and/or solid refractory-type material. That invention included an elongated member which serves the dual function of a feeder for particulate ingot-forming material and of a burner for melting that material. U.S. Pat. No. 4,188,201 further describes one embodiment of the apparatus as including a split tube concentric with the hollow interior or the feeder/burner and rotatable and slidable therein. The split in the tube allows for convenient filling of the tube with the particulate feed simultaneous with insertion of the tube into the furnace. By rotation of the split tube the particulate material could be discharged by gravity through a slot in the feeder/burner. The discharged material clings to the rotating inner surface of the housing due to centrifugal force and is carried to an upper portion where it is melted by flames emanating from orifices spaced along the surface of the feeder/burner opposite the discharge slot.
While the apparatus disclosed in my earlier patent U.S. Pat. No. 4,188,201 has proven admirably suited for producing ingots from a particulate material 50 microns in size and larger, difficulties have been encountered in utilizing materials smaller than 50 microns. In view of the ready availability of silica raw materials of particle sizes within the range of 1-50 microns in various areas of the world, a need has existed for a new apparatus capable of converting such materials into high quality ingots.